1. Field of the Invention
The present invention relates generally to the field of disc drive storage, and more particularly to improved corrosion resistant magnetic media used in disc drives.
2. Description of the Related Art
Computer disc drives commonly use components made out of thin films to store information. Both the read-write element and the magnetic storage media of disc drives are typically made from thin films.
FIG. 1A is an illustration showing the layers of a conventional magnetic media structure including a substrate 105, a seed layer 109, a magnetic layer 113, a diamond like carbon (DLC) protective layer 117, and a lube layer 121. The initial layer of the media structure is the substrate 105, which is typically made of nickel-phosphorous plated aluminum or glass that has been textured. The seed layer 109, typically made of chromium, is a thin film that is deposited onto the substrate 105 creating an interface of intermixed substrate 105 layer molecules and seed layer 109 molecules between the two. The magnetic layer 113, typically made of a magnetic alloy containing cobalt (Co), platinum (Pt) and chromium (Cr), is a thin film deposited on top of the seed layer 109 creating a second interface of intermixed seed layer 109 molecules and magnetic layer 113 molecules between the two. The DLC protective layer 117, typically made of carbon and hydrogen, is a thin film that is deposited on top of the magnetic layer 113 creating a third interface of intermixed magnetic layer 113 molecules and DLC protective layer 117 molecules between the two. Finally the lube layer 121, which is a lubricant typically made of a polymer containing carbon (C) and fluorine (F) and oxygen (O), is deposited on top of the DLC protective layer 117 creating a fourth interface of intermixed DLC protective layer 117 molecules and lube layer 121 molecules.
The durability and reliability of recording media is achieved primarily by the application of the DLC protective layer 117 and the lube layer 121. The DLC protective layer 117 is typically an amorphous film called diamond like carbon (DLC), which contains carbon and hydrogen and exhibits properties between those of graphite and diamond. Thin layers of DLC are deposited on disks using conventional thin film deposition techniques such as ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering or chemical vapor deposition (CVD). During the deposition process, adjusting sputtering gas mixtures of argon and hydrogen varies the concentrations of hydrogen found in the DLC. Since typical thicknesses of DLC protective layer 117, are less than 100 Angstroms, lube layer 121 is deposited on top of the DLC protective layer 117, for added protection, lubrication and enhanced disk drive reliability. Lube layer 121 further reduces wear of the disc due to contact with the magnetic head assembly.
FIG. 1B is an illustration showing an enlarged view of the DLC protective layer 117 with pinholes that allow moisture to penetrate through the DLC protective layer 117 and cause corrosion. DLC protective layer 117 includes first pinhole 130, second pinhole 132, third pinhole 134, fourth pinhole 136, and fifth pinhole 138. Water molecules 140 condense on the surface of DLC protective layer 117 and migrate down into the pinholes. Some of the pinholes are deeper than others. Water molecules can migrate down the deeper holes and corrode the magnetic layer 115. Although, the deeper pinholes have a higher chance of causing corrosion in the magnetic layer, corrosion can still occur when water molecules are trapped in the more shallow pinholes.
One way water molecules 140 condense on the surface of the DLC protective layer and migrate down the pinholes is when the magnetic media structure is taken out of the vacuum chamber and transported to the lubrication station where the lube layer 121 is deposited over the DLC protective layer 117. This transfer process usually involves moving the magnetic media structure without the lube layer 121 in an ambient atmosphere that contains moisture. Once the water molecules 140 have condensed on the surface of the DLC protective layer 117 they will be trapped there by the subsequently lube layer 121 if they are not removed before applying the lube layer 121. It is important to note that even if the water molecules 140 are removed, the lube layer 121 must be applied before the water molecules re-condense on the surface DLC protective layer 117. This can be a difficult task considering that the lubrication process is usually done by dipping the media in a tank of lubricant material, as is further discussed with reference to FIG. 1C below.
FIG. 1C is a flow chart showing the typical steps used to deposit a carbon overcoat and lubrication layer of the magnetic media structure shown in FIG. 1A. The process begins with step 150 by transferring a partially complete media with substrate 105 and seed layer 109, into a vacuum chamber. The transferring process typically involves moving a disk, after depositing the seed layer 109 on it, into a deposition chamber used to deposit metals that make up the magnetic layer 113 without taking it out of vacuum. Next in step 155, the magnetic layer 113 is deposited onto the seed layer 109 using conventional thin film deposition techniques such as sputtering, CVD, PVD etc. The magnetic layer 113 can be a single layer or can comprise multiple layers of both magnetic and non-magnetic materials. For example a typical magnetic layer can consist of 20 bi-layers consecutively stacked on top of each other with each bi-layer consisting of a magnetic layer and a non-magnetic layer. These materials are all deposited in step 155 to make up the magnetic layer.
Next in step 160, the substrate with the magnetic layer 113 is moved to the protective layer deposition chamber where a protective overcoat layer 117 is deposited on the magnetic layer 113. In step 160, the protective layer 117 consisting of an amorphous carbon is deposited over the partially complete media. Typically the amorphous carbon layer is diamond like carbon (DLC) that has been deposited by conventional sputter deposition techniques. Next in step 165, the amorphous carbon is removed from the deposition chamber and moved into a lubrication station. Typically, this involves removing the magnetic media with a carbon containing overcoat from the vacuum chamber and moving it in atmosphere to the lubrication station. Next in step 170 the protective overcoat 117 is coated with a lube layer 121 using a dipping process wherein the magnetic media having a protective overcoat is dipped into a bath of lubricant and the lubricant is consequently drained from the bath leaving a layer of lubricant on the protective overcoat 117. The lubricant can contain Moresco lubricant or PFPE. Finally, in step 175 the lubed magnetic media is transferred to the next manufacturing operation.
In step 160, the lube layer 121 can be applied using several processes including dipping the magnetic media, which has a protective layer 117, into a tank of lubricant fluid or vapor lubing the disk. If the lube layer 121 is applied with a dipping process, the magnetic media with protective layer 117 is first taken out of vacuum and dipped into a tank of lubricant fluid.
In the dipping process, lube layer 121 is typically applied evenly over the disc, as a thin film, by dipping the discs in a bath containing a mixture of a few percent of the lubricant in a solvent and gradually draining the mixture from the bath at a controlled rate. The solvent remaining on the disc evaporates and leaves behind a layer of lubricant less than 100 Angstroms.
When the magnetic media containing amorphous carbon is removed from the deposition chamber and moved into a lubrication station, in step 165, the exposed carbon layer is subjected to moisture, which causes corrosion. Moisture is one of the indispensable ingredients for media corrosion at typical drive operation environments. Moreover, moisture that penetrates the carbon layer and reaches the magnetic layer is one of the most likely causes of corrosion in hard disk drives. As carbon layer become thinner this problem becomes more serious because it is easier for moisture to penetrate through the thinner carbon layer and corrode the magnetic layer. Performance of hard disk drives is heavily dependent on the corrosion resistance of the media.
Therefore what is needed is a system and method that overcomes corrosion problems by stopping and/or inhibiting moisture from penetrating through the carbon layer into the magnetic layer by diffusion or other methods. Additionally, a system and method that reduces corrosion problems of a magnetic disk is needed that prevents moisture from diffusing through both the carbon protective layer and the lubricant overcoat.